Polyamide concentrates containing sulphonate groups

ABSTRACT

The invention relates to high molecular weight polycaprolactams containing monomeric units of the general formulae (I) and (II): ##EQU1## in which: M is an alkali metal; and 
     R is an alkylene radical having from 4 to 12 carbon atoms or the radical, ##SPC1## 
     Where M is as defined above, 
     The polymer having a relative solution viscosity of from 1.1 to 3.5 (as measured on solutions of 1 g of polyamide in 100 ml of m-cresol at 25°C) and containing sulphonate groups in a concentration range of from 40 to 2000 mval per kilogram of polymer.

This invention relates to polyamide concentrates containing sulphonategroups and in particular to modified polycaprolactams which can be dyedwith basic dyes and processed from the melt to form shaped articles,such as films or fibres.

It is known that nylon-6,6 can be modified by co-condensation withmonomers containing sulphonate groups, for example salts of5-sulphoisophthalic acid or salt of N-sulphoalkylhexamethylene diamine,and that shaped structures of these co-condensates can be dyed withbasic dyes, (cf. for example U.S. Pat. Nos. 3,184,436, 3,454,535 orDT-OS No. 1,593,903).

By contrast, nylon-6 cannot be modified in this way because theaforementioned salts of the sulphonates are insoluble in caprolactam,are deposited in polymerisation apparatus and spinning units and do notallow trouble-free production and further processing of the polymer (cf.DT-OS No. 2,215,515, page 1).

Hitherto, all that has been known is that small quantities of a salt ofN-sulphobutylhexamethylene diamine and azelaic acid or the dimeric acidof oleic acid are soluble in caprolactam and can be co-condensed (cf.DT-OS No. 2,215,515).

It has now been found that caprolactam can be polycondensed withN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine in the form of abis-alkali metal salt or even in the form of an internal salt with adicarboxylic acid, for example adipic acid, to form completelyhomogeneous, fusible polycaprolactams which can contain up to 2000 mval.of sulphonate groups per kilogram. It is surprising that, by usingN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine, which can readilybe obtained by a hitherto unknown process from 2-sulphonatobenzaldehydeand hexamethylene diamine, followed by catalytic hydrogenation,polycaprolactum can be modified with sulphonate groups in wideconcentration range to enable it to be dyed with basic dyes, without anyof the known production and processing difficulties attributable toinsoluble constituents. The polycaprolactams having very high sulphonateconcentrations, so-called "concentrates", which can be obtained for thefirst time in this way, can be added to unmodified polycaprolactamimmediately before the shaping or forming process in the particularquantity required to impart dyeability with basic dyes.

Accordingly, the present invention provides new high molecular weightpolycaprolactams which are characterised in that

i. they contain structural elements corresponding to the formulae (I)and (II) ##EQU2## in which M represents an alkali metal; and

R represents an alkylene radical having from 4 to 12 carbon atoms or theradical ##SPC2##

where M is already defined,

ii. they have relative solution viscosities of from 1.1 to 3.5 (asmeasured on solutions of 1 g of polyamide in 100 ml of cresol at 25°C),and

iii. they contain sulphonate groups in a concentration range of from 40to 2000 millival per kilogram of polymer.

These polycaprolactams modified with sulphonate groups can be preparedeither

a. by polycondensing the bis-alkali metal salt ofN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine ##SPC3##

in which

M is as defined above,

with a stoichiometric quantity or, preferably, with an excess of adicarboxylic acid corresponding to the formula

    HOOC--R--COOH

in which

R is as defined above,

together with caprolactam and with an equivalent quantity or,preferably, with a deficit of hexamethylene diamine, based on an excessof dicarboxylic acid, in the melt at temperatures in the range of from100° to 300°C, in the absence of oxygen, in an inert-gas atmosphere andunder pressures in the range of from 20 atms to 0.001 Torr; or

b. by precondensing the bis-alkali metal salt of theN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine ##SPC4##

in which

M is as defined above,

optionally in admixture with hexamethylene diamine, in aqueous solutionwith a dicarboxylic acid ester corresponding to the formula

    R.sub.1 --OOC--R--COOR.sub.1

in which

R is as defined above, and

R₁ represents a lower alkyl radical having from 1 to 5 carbon atoms,

preferably with an excess in a molar ratio of from 1 : 2 to 1 : 4, inthe presence of an inert gas, at normal pressure and at temperatures ofup to 100°C, or under pressure at higher temperatures, and addingcaprolactam and an equivalent quantity, or even a deficit, ofhexamethylene diamine, based on an excess of dicarboxylic acid, to theprecondensate thus formed, distilling off the water at temperatures inthe range of from 100° to 140°C and polycondensing the mixture in themelt at temperatures in the range of from 100° to 300°C, in the absenceof oxygen, in an inert-gas atmosphere and under pressures of from 20atms to 0.001 Torr; or

c. polycondensing the internal salt ofN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine ##SPC5##

with an equivalent quantity of a bis-alkali metal adipate

    MOOC--(CH.sub.2).sub.4 --COOM

in which

M is as defined above,

and optionally with another dicarboxylic acid or dicarboxylic acid esterof the formula

    R.sub.1 --OOC--R--COOR.sub.1

in which

R and R₁ are as defined above,

and the stoichiometric quantity of hexamethylene diamine, optionallyeven a deficit, together with caprolactam in the melt in the same way asdescribed in (a); or

d. by converting the inner salt in aqueous dispersion with an excess ofhexamethylene diamine into a soluble salt in the presence of an inertgas, in the absence of pressure and at temperatures of up to 100°C, orunder pressure at higher temperatures, adding to the resulting aqueoussolution caprolactam, alkali metal adipate in a quantity based on theinner salt and a dicarboxylic acid or dicarboxylic acid ester ordicarboxylic acid or dicarboxylic acid ester mixture of the formula

    R.sub.1 --OOC--R--COOR.sub.1

in which

R and R₁ are as defined above,

in an equivalent quantity or, preferably in an excess, based on thehexamethylene diamine, distilling off the water at temperatures in therange of from 100° to 140°C and polycondensing the mixture in the meltin the same way as described in (a).

The disodium salt is preferably used as the alkali metal salt ofN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine.

The alkali metal salts and the internal salts are prepared by reacting2-sulphonatobenzaldehyde with hexamethylene diamine instoichiometrically equivalent quantities, preferably with an excess of2-sulphonatobenzaldehyde, either in a dispersion, such as, for example,in benzene or toluene, or preferably in solution, such as, for example,in N-methylpyrrolidone, methanol or water, in the presence of acondensation catalyst, for example acetic acid, to form the Schiff'sbase which is then catalytically hydrogenated using a hydrogenationcatalyst, for example Raney nickel, and hydrogen (even without previousisolation where condensation is carried out in solution), to formN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine: ##SPC6##

The internal salt can be isolated by acidifying an aqueous or methanolichydrogenation solution, because it is substantially insoluble in thesesolvents. By adding a base, the internal salt can be converted back intothe external salt form. The yields obtained over both stages are in therange of from 85 to 97%.

The N,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine or its internalsalt are used in such quantities, optionally together with adicarboxylic acid containing sulphonato groups, for example5-sulphonatoisophthalic acid, that the concentration of sulphonategroups in the polycaprolactams according to the invention is in therange of from 40 to 2000 mval and preferably from 80 to 1500 mval per1000 g of polymer.

If the polycaprolactams according to the invention obtained by theprocess described in (a) to (b) are directly introduced at the spinningstage, the ratio of amine to carboxyl groups is increased slightlybeyond equivalence in favour of the carboxyl groups, in order to obtainadequate reservation with respect to acid dyes. Accordingly, the excessof dicarboxylic acid can be in the range up to 3 mol %.

In order to provide an already full condensed, unmodifiedpolycaprolactam with an affinity for basic dyes, a modifiedpolycaprolactam according to the invention can be added in specificquantities to the unmodified polycaprolactam just before the spinningoperation, i.e. before the mixture reaches the spinneret. Where thisprocedure is adopted, it is best to use a polycaprolactam having a highsulphonate concentration, a so-called "concentrate", in order to keepthe quantities to be added as small as possible. It is also favourable,in the interests of reservation with respect to acid dyes, to use anexcess of up to 10 mol % of dicarboxylic acid for polycondensation. Inthis way, the property spectrum of the original polyamide is onlyslightly modified. In this way, it is readily possible to extrudeconcentrates containing up to 2000 mval of sulphonate groups per 1000 gof polymer into homogeneous, granulatable strands which are particularlyconvenient to introduce. The end products are filaments and fibres whichhave an excellent affinity for basic dyes and a good reservation withrespect to acid dyes.

The relative solution viscosities η rel. quoted in the followingExamples were measured at 25°C on solutions of 1 g of material in 100 mlm-cresol.

The parts by weight used in the Examples are to parts by volume askilograms to litres.

The following Examples are to further illustrate the invention withoutlimiting it.

EXAMPLE 1 Preparation of the disodium salt ofN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine ##SPC7##

a. In a reaction vessel equipped with a water separator, a mixture of208.0 parts by weight of the sodium salt of 2-sulphonatobenzaldehyde,58.0 parts by weight of hexamethylene diamine, 2.5 parts by weight ofacetic acid and 900 parts by volume of toluene, is heated with stirringfor 8 hours until no more water is azeotropically separated off. Thepure white deposit is filtered under suction, washed with toluene anddried in vacuo at 80°C.

Yield: 247.5 parts by weight (= 99.7% of the theoretical), m.p.:190°-206°C.

b. 247.5 parts by weight of the bis-Schiff's base prepared in accordancewith (a) are dissolved in 2000 parts by volume of methanol, 30 parts byweight of Raney nickel "B" are added and the mixture is hydrogenated for3.5 hours in a hydrogenation autoclave at a temperature of 112°C andunder a hydrogen pressure of 100 atms. The solution is filtered off fromthe catalyst and concentrated to dryness.

Yield: 235.3 parts by weight (= 94.3% of the theoretical), m.p.:140°-146°C.

    ______________________________________                                        Analysis C       H       O     N     S     Na                                          %       %       %     %     %     %                                  ______________________________________                                        calculated:                                                                            48.0    5.2     19.2  5.6   12.8  9.2                                found:   47.8    5.1     19.2  5.2   12.1  8.8                                ______________________________________                                    

EXAMPLE 2 Preparation of the internal salt ofN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine ##SPC8##

A solution of 1160 parts by weight of hexamethylene diamine, 4576 partsby weight of the sodium salt of 2-sulphonatobenzaldehyde and 50 parts byweight of glacial acetic acid in 12,000 parts by weight of water, isheated under reflux for 3 hours in a reaction vessel equipped with astirrer and reflux condenser. The solution is then hydrogenated for 2.5hours at 75°C under a hydrogen pressure of 60 atms in a hydrogenationautoclave to which 100 parts by weight of Raney nickel B are added.After the hydrogenation catalyst has been separated off, the aqueoussolution is acidified with hydrochloric acid. The deposit formed isfiltered under suction and washed with water until neutral.

Yield: 4031 parts by weight (88.4% of the theoretical). m.p.: does notmelt up to 300°C

    Analysis C        H       O      N      S                                              %        %       %      %      %                                     ______________________________________                                        calculated:                                                                            52.6     6.1     21.1   6.1    14.0                                  found:   52.2     6.3     21.8   6.3    13.8                                  ______________________________________                                    

EXAMPLE 3

In a polycondensation apparatus, a mixture of 47,650 parts by weight ofε-caprolactam, 1310 parts by weight of ε-aminocaproic acid, 912 parts byweight of the internal salt ofN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine, 380 parts by weightof sodium adipate and 50 parts by weight of phosphorous acid, is heatedfor 2.5 hours to 270°while nitrogen is passed over, and is condensedwith stirring for 4 hours. The highly viscous melt is spun through awater bath into strands which are granulated. The granulate is extractedwith water at 80°C and dried in a tumbler dryer at 100°C. After thistreatment, the polymer has the following properties:

Melt viscosity (at 260°C): 3620 poises

Melt viscosity (at 280°C): 2140 poises

Relative viscosity η rel. = 2.735

Water content = 0.040%

Softening point = 221°C

Sulphur content = 80 mval of sulphonate groups/kg of polymer.

Filaments produced from this polyamide can be dyed to form deep colourswith basic dyes, for example: ##SPC9##

EXAMPLE 4

In a polycondensation apparatus, a mixture of 4000 parts by weight ofwater, 1140 parts by weight of the internal salt ofN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine and 435 parts byweight of hexamethylene diamine, is reacted with stirring for a periodof 2 hours at 100° C while nitrogen is passed over. 2605 parts by weightof ε-caprolactam, 475 parts by weight of disodium adipate, 570 parts byweight of adipic acid and 5 parts by weight of phosphorous acid, arethen added at around 80°C. The solution is then heated with stirring to200°C with the vessel closed. After venting, the temperature isincreased to 275°C. After stirring for 1.5 hours in the presence ofnitrogen under these conditions, the pressure is gradually reduced to 15Torr over a period of 2 hours, followed by condensation for a further 2hours. The highly viscous melt is then extruded and the strands arepassed over a drying belt and subsequently granulated. The homogenous,colourless concentrate has the following properties:

Melt viscosity (at 260°C): 1165 poises

Melt viscosity (at 240°C): 2250 poises

Relative viscosity η rel. = 1.94

Water content: 0.037%

Softening range: 165°-172°C

Sulphur content = 1015 mval of sulphonate groups/kg of polymer.

The addition of 8% by weight of this concentrate to an unmodifiednylon-6 before spinning ultimately results in the formation of filamentswhich can be dyed to deep colours with basic dyes, for example with adye corresponding to the formula: ##SPC10##

These filaments also show good reservation with respect to acid dyes.

EXAMPLE 5

In a polycondensation apparatus, 1776 parts by weight of the sodium saltof 5-sulphoisophthalic acid dimethyl ester, 1114 parts by weight ofhexamethylene diamine and 1200 parts by weight of the disodium salt ofN,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine, are heated underreflux for 2 hours in 10,000 parts by weight of water while nitrogen ispassed over. On completion of precondensation, 1272 parts by weight ofsebacic acid, 5239 parts by weight of caprolactam and 10 parts by weightof phosphorous acid are added to the solution, and the closed vessel isheated to 200°C so that the internal pressure amounts to 16 atms. After1 hour under these conditions, the vessel is vented over a period of 3to 5 hours. It is then flushed with nitrogen, the temperature isincreased to 270°C and the pressure is gradually reduced to 5 Torr.After 8 hours under these conditions, condensation is terminated, theviscous melt is extruded and the strands are passed over a drying beltand granulated by a following granulator. The homogeneous colourlessconcentrate has the following properties:

Melt viscosity (at 260°C): 1423 poises

Melt viscosity (at 240°C): 2644 poises

Relative viscosity η rel. = 2.04

Water content: 0.051%

Softening range: 162°-169°C

Sulphur content: 1085 mval of sulphonate groups per kg of polymer.

If 7% by weight of a concentrate of this kind are added to an unmodifiednylon-6 shortly before spinning, the filaments obtained and the articlesproduced from them can be dyed to deep colours with basic dyes, forexample: ##SPC11##

The filaments moreover show good reservation with respect to acid dyes.

EXAMPLE 6

In a polycondensation apparatus, 3420 parts by weight of the inner saltof N,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine and 1305 parts byweight of hexamethylene diamine are heated under nitrogen while stirringto 100°C in 10,000 parts by weight of water until a clear solution isformed. 1708 parts by weight of adipic acid, 1425 parts by weight ofdisodium adipate, 2817 parts by weight of caprolactam and 10 parts byweight of phosphorous acid, are then added to the solution. By heatingto 140°C, the water is removed by distillation. The temperature is thengradually increased to 275°C. Condensation is continued for 3 hoursunder these conditions, after which the pressure is gradually reduced to15 Torr and condensation is completed over a period of a further 4hours. The clear, colourless melt is granulated as described in Example5. The concentrate shows the following properties:

Melt viscosity (at 260°C): 1244 poises

Melt viscosity (at 240°C): 2851 poises

Relative viscosity η rel. = 1.79

Water content: 0.032%

Softening range: 191°-198°C

Sulphur content: 1496 mval of sulphonate groups per kg of polymer.

The addition of 6% by weight of this concentrate to an unmodifiednylon-6 leads after spinning to filaments which can be dyed to deepcolours with basic dyes, as described in Examples 3, 4 and 5, and whichshow good reservation with respect to acid dyes.

EXAMPLE 7

In a condensation apparatus, 456.0 parts by weight of the internal saltof N,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine and 174.0 partsby weight of hexamethylene diamine are heated under nitrogen withstirring to 100°C in 1000 parts by weight of water until a clearsolution is formed. 22.8 parts by weight of adipic acid, 190.0 parts byweight of disodium adipate, 50.1 parts by weight of caprolactam and 10parts by weight of phosphorous acid are then added, the water removed bydistillation and the temperature is increased to 280°C. Condensation iscarried out at a temperature of 280°C over a period of 2.5 hours undernormal pressure and over a period of 4 hours at 15 Torr. A clear,homogeneous, colourless viscous melt is obtained, and is subsequentlygranulated in the same way as described in Example 5. The concentratehas the following properties:

Melt viscosity (at 260°C): 2015 poises

Melt viscosity (at 240°C): 2965 poises

Relative viscosity η rel. = 2.33

Water content: 0.061%

Softening range: 195°-204°C

Sulphur content: 1996 mval of sulphonate groups per kg of polymer.

If only 4% by weight of this concentrate are added to an unmodifiednylon-6 before spinning, the filaments obtained can be dyed to deepcolours with basic dyes whilst at the same time they show goodreservation with respect to acid dyes.

What we claim is:
 1. High molecular weight polycaprolactams containingstructural elements of the general formulae (I), (II) and (III) ##EQU3##in which: M is an alkali metal; andR is an alkylene radical having from4 to 12 carbon atoms or the radical, ##SPC12## where M is as definedabove,the polycaprolactams having relative solution viscosities of from1.1 to 3.5 (as measured on solutions of 1 g of polyamide in 100 ml ofm-cresol at 25°C) and containing sulphonate groups in a concentrationrange of
 2. High molecular weight pollycaprolactams containingstructural elements of the general formulae (I), (II), (III) and (V)##EQU4## having relative solution viscosities of from 1.1 to 3.5 (asmeasured on solutions of 1 g of polyamide in 100 ml of m-cresol at 25°C)and containing sulphonate groups in a concentration range of from 40 to2000 mval per kilogram of polymer.
 3. A process for the production ofhomogeneous polycaprolactams containing structural elements of thegeneral formulae (I) and (II): ##EQU5## in which M is an alkali metal;andR is an alkylene radical having from 4 to 12 carbon atoms or theradical ##SPC13## where M is as defined above,wherein either a. thebis-alkali metal salt of N,N'-bis-(2-sulphonatobenzyl)-hexamethylenediamine ##SPC14## in whichM is as defined above, is polycondensed withthe stoichiometric quantity, or preferably with an excess, of adicarboxylic acid corresponding to the formula

    HOOC--R--COOH

in whichR is as defined above, and caprolactam and, otpionally, anequivalent quantity or, preferably, a deficit of hexamethylene diamine,based on an excess of dicarboxylic acid, in the melt at temperatures inthe range of from 100° to 300°C, in the absence of oxygen, in an inertgas atmosphere and under pressures of from 20 atms to 0.0001 Torr; or b.The bis-alkali metal salt of N,N'-bis-(2-sulphonatobenzyl)-hexamethylenediamine ##SPC15## in whichM is as defined above, is precondensed inaqueous solution with a dicarboxylic acid ester corresponding to theformula

    R.sub.1 --OOC--R--COOR.sub.1

in whichR is as defined above R₁ represents a lower alkyl radical havingfrom 1 to 5 carbon atoms, preferably an excess in a molar ratio of from1 : 2 to 1 : 4, in the presence of an inert gas, in the absence ofpressure at temperatures of up to 100°C or under pressure at highertemperatures, and caprolactam and, optionally, an equivalent quantity oreven a deficit of hexamethylene diamine, based on an excess ofdicarboxylic acid, is added to the precondensate thus obtained, thewater is distilled off at temperatures in the range of from 100° to140°C and the mixture is polycondensed in the melt at temperatures offrom 100° to 300°C, in the absence of oxygen, in an inert gas atmosphereand under pressures of from 20 atms to 0.001 Torr; or c. the internalsalt of N,N'-bis-(2-sulphonatobenzyl)-hexamethylene diamine ##SPC16## ispolycondensed either with the equivalent quantity of a bis-alkali metaladipate

    MOOC--(CH.sub.2).sub.4 COOM

in whichM is as defined above, and optionally with another dicarboxylicacid or dicarboxylic acid ester of the formula

    R.sub.1 --OOC--R--COOR.sub.1

in whichR and R₁ are as defined above, and with the stoichiometricquantity of hexamethylene diamine, optionally even a deficit, togetherwith caprolactam, in the melt in the same way as described in (a); or d.the internal salt in aqueous dispersion is converted with an excess ofhexamethylene diamine in the presence of an inert gas in the absence ofpressure at temperatures of up to 100°C or under pressure at highertemperatures, into a soluble salt, and the aqueous solution obtained hasadded to it caprolactam, alkali metal adipate in a quantity based on theinternal salt and a dicarboxylic acid or dicarboxylic acid ester ordicarboxylic acid or dicarboxylic acid ester mixture of the formula

    R.sub.1 --OOC--R--COOR.sub.1

in whichR and R₁ are as defined above, in an equivalent quantity or,preferably, even in an excess, based on the hexamethylene diamine, thewater is distilled off at temperatures of from 100° to 140°C and themixture is polycondensed in the melt in the same way as described in(a).